johnson 15 cranks, runs for 10 seconds and dies

jacobgiles · Oct 20, 2010

i have a 76 model johnson 15 that i just bought. it cranks up and runs, then dies after about 10-15 seconds. sometimes i can get it to run longer by working the throttle. after it runs 2 or 3 times, the plugs are soaked with fuel. i pulled the carb and rebuilt it. (there was no idle needle bushing in there, but i put one in.) the carb is still flooding. i know the previous owner put a new fuel pump on it and claims the motor ran good after. he stated that the motor ran good when he last used it and that it just was sitting up too long and needed the carb gone though. when i got the motor the fuel was about 6 months old and smelled terrible.

im out of ideas. any advice is greatly appreciated.

oldcatamount · Oct 20, 2010

Re: johnson 15 cranks, runs for 10 seconds and dies

When you re-built the carb, did you replace the float valve and seat and did you replace and re-adjust the float itself?

jmendoza · Oct 20, 2010

Re: johnson 15 cranks, runs for 10 seconds and dies

Well, from what you said, it would be safe to get rid of that fuel and use fresh gasoline, but that is most likely not all of your problem. That bushing on the needle, if it's not there or damaged will cause a uncontrollable rich low speed problem that cannot be corrected by the needle adjustment, we just spent 7 pages figuring that out for another guy! Go ahead and replace it, and give it another try. Needle setting is about 1.5 turns out as a start point.
The low speed needle is adjusted once the engine is warm and set with the engine in forward gear, in the water on a boat, at low speed. If you set it at idle in neutral, it will be too lean when you go into gear.

jacobgiles · Oct 20, 2010

Re: johnson 15 cranks, runs for 10 seconds and dies

oldcatamount said:
When you re-built the carb, did you replace the float valve and seat and did you replace and re-adjust the float itself?

yes, i did replace the float valve and seat and i re-adjusted the float to be level with the carb when i held it upside down.

jacobgiles · Oct 20, 2010

Re: johnson 15 cranks, runs for 10 seconds and dies

jmendoza said:
Well, from what you said, it would be safe to get rid of that fuel and use fresh gasoline, but that is most likely not all of your problem. That bushing on the needle, if it's not there or damaged will cause a uncontrollable rich low speed problem that cannot be corrected by the needle adjustment, we just spent 7 pages figuring that out for another guy! Go ahead and replace it, and give it another try. Needle setting is about 1.5 turns out as a start point.
The low speed needle is adjusted once the engine is warm and set with the engine in forward gear, in the water on a boat, at low speed. If you set it at idle in neutral, it will be too lean when you go into gear.

i have a new fuel tank and line/ primer bulb with fresh 93 octane mixed 50:1. when i rebuilt the carb i installed a new idle needle bushing and i have the needle 1.5 turns out and the knob is pointed straight down so i can easily adjust either way.

thanks for the tips and suggestions and please keep them coming.

jacobgiles · Oct 20, 2010

Re: johnson 15 cranks, runs for 10 seconds and dies

another thing i noticed today while i was trying to run it is that the fuel primer bulb is not staying firm. is it supposed to?

bktheking · Oct 20, 2010

Re: johnson 15 cranks, runs for 10 seconds and dies

No it isn't supposed to, fuel flows while running, the bulb only gets hard cause the carb fills up and can't take any more fuel cause the float shuts off the fuel flow via the needle and seat, in a nutshell.

bktheking · Oct 20, 2010

Re: johnson 15 cranks, runs for 10 seconds and dies

76 is a points motor, how strong is the spark? Spark and fuel go hand in hand during idle, I've cleaned carbs spotless only to find out points are dirty causing weak spark which in turn causes crappy to no idle.

jacobgiles · Oct 20, 2010

Re: johnson 15 cranks, runs for 10 seconds and dies

bktheking said:
76 is a points motor, how strong is the spark? Spark and fuel go hand in hand during idle, I've cleaned carbs spotless only to find out points are dirty causing weak spark which in turn causes crappy to no idle.

how can i check to see how strong my spark is? i have never worked on points before. is there a tutorial on how to reset/ replace the points?

bktheking · Oct 20, 2010

Re: johnson 15 cranks, runs for 10 seconds and dies

A spark tester , the one you can adjust the distance. Or you could take an old plug and increase the gap to say 50- 60 thou. There should be a points rundown in the top secret file listed at the top of the forum. If spark is good and strong then stick with the carb troubleshooting.

jacobgiles · Oct 20, 2010

Re: johnson 15 cranks, runs for 10 seconds and dies

i will get a tester and post results tomorrow afternoon. thanks for the help!

by the way compression is 100 and 95.

OptsyEagle · Oct 20, 2010

Re: johnson 15 cranks, runs for 10 seconds and dies

You say it did not have an idle bushing in there. How do you know this? I know I could never see to the end of the carb jet to determine if one was in there, even with a flashlight. They are not prone to falling out on there own and I can't see why anyone would purposely take one out and not put one back in. I doubt it would work as well that way either. Perhaps you now have 2 idle adjustment bushings in there. They don't work like dixie cups.

jacobgiles · Oct 20, 2010

Re: johnson 15 cranks, runs for 10 seconds and dies

i used a led flashlight. before you could see the metal, now you can see the bushing i put in. i am certain there is only 1 in there.

johnson 15 cranks, runs for 10 seconds and dies

Cadet

Lieutenant Commander

Petty Officer 1st Class

Cadet

Cadet

Cadet

Vice Admiral

Vice Admiral

Cadet

Vice Admiral

Cadet

Lieutenant

Cadet